Using LT3798 sample circuit for 5 V 3 A output

I am interested in using the given example circuit (linked below) for my senior design project and was wondering what transformer (part # off the shelf) I could use to provide 5 V 3 A output? (Preferably from Wurth Electronic) Additionally, I am interesting in using this for a 5 V 3 A output, what changes might I need to make to the circuit in order to get 3 A output instead of 2.2? Thank you very much for your time.
  • This converter was done for a specific application, with emphasis on efficiency and minimum power consumption at no load.

    There is a transformer from Wurth Electronics, 750811101, which can do 5V at 3A, but needs to be tested with the configuration called out.

    The following are recommended changes to test the converter (please refer to the schematic for designators):

    1. Double the value of C3 (input cap).

    2. Change value of R6 to 4.32K (feedback resistor).

    3. Double or triple the total output capacitance value. Ensure capacitors have at least 4.5A of ripple current capability.

    Other minor value changes might be needed, but the above changes should bring you close to the goal.

    Again, testing is required to ensure converter meets your requirements.

  • I can't find any Ltspice files for Wurth 750811101 but I do have them for 750811618 and 750811611 which I was told by Wurth should also work for this application. I've been playing with the circuit values but can't seem to get 5 V 3 A from either of these transformers. What changes would you suggest in the case that I was using one of those two?

    Thank you so much for replying with such helpful information! 

  • I would suggest you try the 750811611 option, with secondary windings in parallel. The leakage inductance is on the high side, but the other option is not much better.

    Follow the list I gave before, except increase R6 to about 7K, instead of 4.32K. (might have to readjust this resistor later).

    To make life easier, I would not start with the circuits in the dashed boxes, for now. You can add these options later, after you get the converter working.

    To implement this suggestion, connect IC bias and output rectification as shown below. You can choose a diode option from the datasheet. Diode might need a heat-sink, once you get 3A of output current.

    Best of luck!

    Cheers!

  • I managed to get 5v and 1.6 A using the circuit shown as 403-5v. I'm unable to get it to 3 A as far as I can tell, is this approach feasible? Additionally, I attempted to make the suggested changes to the circuit and it's completely stopped working (shown as 403-2). Do you have a full schematic I might be able to see for the full wiring layout? 

    403-5v:

    403-2:

    Thanks!!

  • This application is a bit more complicated to be resolved in this manner. If you wish, you can provide your phone number and I can give you a call Monday to discuss further details.

    Or, you can start with our LT3798 simulation circuit, available online, and mainly change the transformer parameters to fit your application.